1. Field of the Invention:
The present invention relates to a process for the manufacture of maleic anhydride by a vapor phase catalytic oxidation of n-butane with molecular oxygen, and, in particular, to a process for the manufacture of maleic anhydride using a phosphorus vanadium oxygen composite catalyst prepared by a specific process and containing specific metals.
2. Description of the Prior Art:
Processes for the manufacture of maleic anhydride by a vapor phase catalytic oxidation of n-butane using molecular oxygen are conventionally well known in the art. Various types of catalysts used in the processes have been proposed or reported. For example, British Patent No. 1,399,560 proposes a phosphorus vanadium-oxygen composite catalyst containing Cr, Fe, Hf, Zr, La, or Ce; U.S. Pat. No. 3,862,146 discloses a phosphorus vandium oxygen composite catalyst containing Zn, Cu, Bi, or Li; and U.S. Pat. No. 3,987,063 describes a phosphorus vanadium oxygen composite catalyst containing Co, Ni, or Cd. In addition, "Shokubai", Vol. 33, No. 2, pp 115-118 (1991) presents a report dealing with the catalytic activity of a phosphorus-vanadium oxygen composite catalyst containing Mo, Sb, Cr, Fe, As, Mn, Sn, Co, Cu, Zn, W, Ca, Mg, Na, K, or Cs. These conventional phosphorus vanadium oxygen composite catalysts containing various kinds of metals proposed or reported heretofore, however, are not satisfactory in their catalytic activity, the selectivity for maleic anhydride, and the like. Improvements in their performances are therefore desired.